1. Field of the Invention
The present invention relates to a rotary damper for use with a toilet lid or a similar angularly movable lid, and more particularly to a self-standing mechanism in such a rotary damper for keeping an angularly movable lid in an upright position against falling movement by gravity.
2. Description of the Prior Art
One known rotary damper with a self-standing mechanism is disclosed in Japanese laid-open patent publication No. 5-180239.
The disclosed rotary damper, which is typically used with a toilet lid, has a cylindrical casing which houses a pair of spring-biased balls and a rotor rotatably disposed in the cylindrical casing and having a pair of diametrically opposite recesses for receiving the spring-biased balls, respectively. The rotor has an axial end coupled to a shaft of the toilet lid. A viscous fluid is sealed in a space between the cylindrical casing and the rotor for damping angular movement of the rotor with respect to the cylindrical casing.
When the toilet lid is manually opened to its upright position by the user, the rotor is angularly moved in one direction about its own axis until the spring-biased balls are received in the recesses, respectively. The spring-biased balls received in the respective recesses retain the toilet lid in the upright position, typically 90.degree. spaced upwardly from the toilet seat on the toilet bowl.
When the toilet lid is manually closed from the upright position by the user, the spring-biased balls are forced out of the respective recesses, and the toilet lid is slowly angularly moved downwardly toward the toilet seat under damping forces produced by the viscous fluid. At the time the spring-biased balls are forced out of the respective recesses, the spring-biased balls frictionally engage edges of the recesses. As the toilet lid is repeatedly opened and closed, the edges of the recesses tend to wear off to a round shape by frictional contact with the spring-biased balls. The round edges of the recesses are ineffective to retain the spring-biased balls firmly in the respective recesses, and hence to hold the toilet lid in the upright position.